1. Field of the Invention
The present invention relates to a touch panel driving circuit and a touch panel including the same, and more particularly, to a driving circuit of a photosensing type touch panel and a touch panel including the driving circuit.
2. Description of the Related Art
Typically, input signals are applied to computers using a mouse, a keyboard, or other input devices. A remote control may also be used to select functions of digital televisions. However, users who are not skilled in using a mouse, keyboard, remote control, or the like have difficulty using these input devices.
Touch panels or touch screens are input devices aimed at users having difficulty using the conventional input devices mentioned above. Input of command signals, which is conventionally performed using a mouse or the like, can be performed by directly contacting a finger, pen, etc. onto a display panel with a touch panel.
Since the command signals can be input by contacting the finger onto the display panel, users having difficulty using input devices such as a mouse and a keyboard can easily use digital devices, such as computers, using such touch panels or touch screens. Touch panels can be classified into several groups based on a method of recognizing an external input: capacitive touch panels; resistive overlay touch panels; infrared beam touch panels; ultrasonic wave touch panels; integral strain gauge touch panels; piezo electric touch panels; photosensing type touch panels; etc.
In a photosensing type touch panel, which includes a photodiode, contact by a finger is recognized by detecting a current generated when light is incident on the photodiode. Photodiodes, which are elements utilized in the photosensing process, may be formed when driving circuits of display panels, such as LCD and OLED display panels, are formed. In addition, the thickness of such a photosensing type touch panel may be decreased since additional layers, which need to be formed outside of a resistive overlay touch panel or a capacitive touch panel, are not necessary.
However, the current generated in the photodiode is affected by the brightness of the light which is incident on the photodiode, and temperature of the photodiode or peripheral regions of the photodiode.
FIG. 1 is a graph of current flowing in a photodiode with respect to the brightness of the light incident on the photodiode, at two different temperatures. The X-axis of the graph represents the brightness of the light incident on the photodiode, and the Y-axis represents current flowing in the photodiode. The upper curve represents current when the temperature is 40° C., and the lower curve represents current when the temperature is 25° C. Referring to FIG. 1, as the temperature increases, a larger amount of current flows in the photodiode at the same brightness.
FIG. 2 is a photographic image showing a temperature increase in peripheral regions of a contact point of a finger on a touch panel due to the heat of the finger. Referring to FIG. 2, temperature is increased in a circular region in the upper right hand corner which is brighter than peripheral regions.
As described above, when a user touches a touch panel with a finger, the temperature of peripheral regions of the contact point of the photodiode is increased by the heat of the finger, and thus the current generated from the photodiode is changed by the temperature increase. As a result, since the current of the photodiode is affected by not only the brightness of the light incident on the photodiode, but also the temperature of the finger, the result of detecting the contact of the finger may cause an error if the effect of the heat of the finger is not considered.